1. Field of the Invention
The present invention relates to an electric motor control device that controls an electric motor having an armature or both of an armature and a field.
2. Description of the Related Art
Generally, an AC electric motor has an armature formed of multiple windings in many cases and this configuration often allows rotation itself to continue in the event of an open phase due to a failure in part of the wirings. This configuration, however, has a problem that adverse effects, such as a desired torque cannot be obtained and a torque ripple is increased, occur frequently.
For the control on the electric motor to be continued in the event of a failure in part of the electric motor, a motor control device described, for example, in JP-A-2009-268332 is formed of a three-phase inverter circuit 10, a neutral voltage detection circuit 15, and a micro-computer 17. The neutral voltage detection circuit 15 is formed of a circuit that detects a neutral voltage across a three-phase AC motor M1. After one phase out of all phases becomes unable to carry a current, the micro-computer 17 determines a variance of a failure state on the basis of an output voltage of the neutral voltage detection circuit 15 and, when the failure state varies, controls the three-phase inverter circuit 10 under a control state corresponding to the varied failure state. Accordingly, even when one phase out of all phases becomes unable to carry a current and the failure state varies afterward, it becomes possible to perform the control corresponding to the failure state that has varied.
The motor control device described in JP-A-2009-268332 performs the control corresponding to the failure state. However, control such that forestalls a failure is not performed. More specifically, this motor control device does not perform control in consideration of temperatures and heat generation, which are chief factors of a failure in an electric motor and an electric motor control device, and therefore has a problem that a failure may possibly occur due to a temperature rise or an increase in heat generation during the control of the electric motor.